Condensation of benzene dicarboxylic acid with formaldehyde to produce tetracarboxydiphenylmethanes



United States Patent This invention relates to a new group ofpolyfunctional compounds and a novel process for the preparation ofthese new materials. More particularly, the invention relates to newpolyfunctional polyaryl compounds prepared by the condensation ofdicarboxyphenyl compounds with aldehydes to preparetetracarboxydiphenylmethanes.

Polyfunctional compounds, that is, compounds which possess more than onefunctional group, are in great demand in the chemical industry due totheir high degree of reactivity and consequent suitability asintermediates in the preparation of many important chemical products.Where the functional groups of the polyfunctional compound are separatedby sufficient space in the molecule, as in the case of polyfunctionaltype polyaryl compounds having at least one functional group on each ofthe aryl nuclei, the compounds are even more desirable because of thehigher degree of stability inherent in the chemical products derivedfrom them.

Polyfunctional compounds which have functional groups distributed onmore than one aryl nucleus have been prepared by various methods knownin the chemical art. Many of the prior processes involve a multiplicityof complicated and expensive steps with resultant low overall yields.By-products formed in these prior art preparations of polyfunctionalcompounds having polyaryl type structures are numerous and complicatethe purification or render the product incapable of separation.

We have discovered that polyfunctional compounds of the polyaryl typehaving two functional groups on each of 'the aryl nuclei can be preparedby heating a dicarboxyphenyl compound with an aldehyde having noa-hydrogen substituent to an elevated temperature in concentratedsulfuric acid, oleum, or liquid sulfur trioxide to effect thecondensation.

It is an object of the present invention to produce a novel class oftetracarboxylic acids. It is a further object of the present inventionto produce a novel class of alkali metal, alkaline earth metal, andamine salts of tetracarboxylic acids. A'further object of the presentinvention is to produce new and novel classes of monoesters, diesters,triesters, and tetraesters of tetracarboxylic acids. Another object ofthe present invention is to prepare tetracarboxylic acids havingimportant applications in the chemical industry. For example, thevarious esters prepared from these tetracarboxylic acids, either aspartial esters or as tetraesters have valuable properties asplasticizers for polymeric resins. The tetracarboxylic acids themselvesfind application in the manufacture of alkyd resins in co-reaction withpolyhydric alcohols and in the manufacture of polyester type resins. Thesalts of these tetracarboxylic acids are highly valuable as chemicalintermediates for the production of surface active agents, waterrepellents, sequestering agents, lubricant additives, etc. These andother objects of the present invention will be discussed in greaterdetail hereinbelow.

The novel tetracarboxylic acids of the present invention can beillustrated by the general formula:

COOH HOOC 3,257,452 Patented June 21, 1966 wherein R representshydrogen, a t-alkyl radical, a cycloalkyl radical, or an aryl radical.This formula is illustrative of the essential substituents of our novelcompounds. It will be understood, of course, that in many instances itwill be desirable to have one or more halogen or alkyl substituents oneach of the aryl nuclei. The partial and tetraesters, and the partialand tetrasalts that can be prepared from the above tetracarboxylic acidsare included within the scope of our present invention.

The novel type compounds of the present invention are prepared by acondensation reaction wherein a dicarboxyphenyl compound reacts with analdehyde selected from the aldehydes that have no a-hydrogen atoms.Suitable dicarboxyphenyl compounds include any of the three isomericbenzene dicarboxylic acids, the corresponding acid chlorides and estersof these acids, e.g., phthalic acid, isophthalic acid, terephthalicacid, phthaloyl chloride, isophthaloyl chloride, terephthaloyl chlorideand the mono and diesters of these dibasic acids. Ordinarily, during thecourse of the condensation reaction and work-up of the product, thedibasic acid derivatives are converted to the dibasic acid. However, forreasons of convenience, and for improved solubility characteristics, itis many times convenient to charge the acid chlorides or esters to thereactor. The selection of an appropriate mono or diester is ordinarilymade by taking into consideration economic factors as well as solubilitycharacteristics. The reaction proceeds in a normal manner with suchesters as monomethyl phthalate, diethyl isophthalate, di-n-propylterephthalate, dibutyl phthalate, mono-Z-ethylhexyl isophthalate,dioctyl terephthalate, etc.

The preparation of our novel tetracarboxydiphenylmethanes can be carriedout using any of the three isomeric benzene dicarboxylic acidscontaining up to three additonal substituents attached to the benzenenucleus. We prefer dicarboxy benzene compounds that can contain up to 3substituents attached to the benzene nucleus, where said substituentsare preferably selected from the group consisting of alkyl radicals ofup to about 12 carbon atoms, and halide radicals where the halide ischloride, bromide or iodide. It will be understood that the substitutedacid chlorides, monoesters, and diesters can also suitably be used. Inthe preparation of our novel compounds, we can use for example:2,4,6-trichloroisophthalic acid, 2,4-dibromoisophthalic acid, dimethyl2- iodoisophthalate, dibutyl 2-methyl-4,6-dichloroisophthalate,isopropyl 2-bromo-4,6-dimethylisophthalate, 2,4,6-tributylisophthalicacid, 2,4-dihexylisophthalic acid, dibutyl- 2-dodecylisophthalate,2,4-dichloroisophthaloyl chloride, 2-decyl-4-chloro-isophthaloylchloride. These representative compounds are merely illustrative of ourpreferred reactants. The corresponding derivatives of phthalic acid,phthalic anhydride, and terephthalic acid can be used as reactants inpreparing our novel compounds.

Our invention is broadly applicable to the condensation of a dicarboxybenzene compound with an aldehyde having no activated hydrogen atom inthe u-position to the carbonyl group. A preferred aldehyde within thisclassification is formaldehyde or one of its equivalents such asparaformaldehyde, trioxymethylene, or dimethoxymethane. Among the otheraldehydes that can be used in the practice of our invention are suchsubstances as trimethylacetaldehyde, (CH CCHO, benzaldehyde, nuclearsubstituted benzaldehydes, etc.

The novel compounds of our invention can be prepared by means of acondensation reaction, as described herein then poured into ice water.

ylmethane results in an attack by the oxidizing agent on the substitutedmethane with a resultant production of a mixture of miscellaneousoxidation products.

Generally, the condensation of the dicarboxy benzene compound with thealdehyde, containing no hydrogen atoms alpha to the carbonyl group, iseffected in a concentrated sulfuric acid medium. We prefer to employ aconcentrated sulfuric acid solution containing at least 90% sulfuricacid. We have further found that the reaction proceeds rapidly in 100%sulfuric acid which contains dissolved sulfur trioxide. These materialsare commonly referred to as oleum, for example oleum refers to 100%sulfuric acid containing 10% free sulfur trioxide. The condensationreaction can be conveniently conducted in oleum containing from about10% to about 65% free S0 If desired, the reaction can be conducted inliquid 100% S0 although operation must of necessity be conducted in apressure vessel to contain the low boiling sulfur trioxide in the liquidphase.

The condensation reaction can be conducted at any temperature within therange of about 50 C. to about 250 C. Of course, at the lowertemperature, the time required will be unduly lengthened. We prefer tocarry out the reaction within about 100 C. to about 200 C., morepreferably in the temperature range from about 100 C. to about 150 C. 1

The use of stoichiometric quantities of the dicarboxy benzene compoundand the aldehyde are desirable; however, since an excess of eitherreactant is readily recoverable, the proportion of reactants used in theoriginal reaction mixture is immaterial. For best yields, however, it ispreferred to employ about 2 moles of the dicarboxy benzene compound permole of the aldehyde. The heating period is comparatively unimportant,some of the tetracarboxydiphenylmethane compound being formed as soon asthe reactants are contacted with the oleum medi um. Optimum yields ofthe tetracarboxydiphenylmethane compound are obtained by conducting theheating for a time of, say, 2 hours to about hours.

We have further discovered that our novel tctracar boxylic acids can beused in the preparation of another series of novel polyfunctionalcompounds. We can use reducing agents such as LiAlI-L, to reduce eitherthe tetracarboxylic acids or the tetraesters derived from these acids toprepare the corresponding tetramethyloldiphenylmethanes or we can useLiBH with the tetraalkyl esters to prepare these same compounds. Whilewe prefer to use lithium aluminum hydride or lithium borohydride forthis reductive step, other well known reducing agents such as copperchromite can also be used. The tetramethyloldiphenylmethanes prepared bythis reductive step can be used in the preparation of alkyd type resins,they can be used in the preparation of polyesters by reaction withpolybasic acids, and they have also found application in the preparationof surface active agents, for example, by reaction with ethylene oxide,propylene oxide, or by reaction with small quantities of propylene oxidefollowed by higher proportions of ethylene oxide.

In order to illustrate some of the various aspects and advantages of theinvention, representative examples are given herein. It will of course,be understood that variations in the particular starting materials, acidconcentrations, reaction times and reaction temperatures and the likecan be made without departing from the invention.

Example 1 A glass reactor equipped with a condenser and thermowell wascharged with 100 ml. of 20% oleum, 33 g. (0.20 mole) isophthalic acidand 3.1 g. (0.10 mole) paraformaldehyde. This mixture was maintained ata temperature between 110 and 119 C. for 6 hours, cooled and The crudemixture which was recovered by filtration, was dissolved in 200' ml.methanol and saturated with HCl gas. During a refluxprecipitated. Themixture was cooled to 10 C. and

filtered to recover the tetramethyl ester of bis(isophthalicacid)methane, MP. 196198 C. The tetramethylester was washed with coldmethanol and recrystallized from zene to give the purified product,melting at 199'200 C. This product, 3,3,5,5-tetracarbomethoxydiphenyLmethane analyzed as follows:

Calculated for C H O C, 63.0; H, 5.0; saponification equivalent, 100.Found: C, 63.17; H, 5.34; saponification equivalent, 100.

The nuclear magnetic resonance spectrum was consistent with the proposedstructure. -In this run the yield of3,3',5,5-tetracarbomethoxydiphenylmethane was 84% based on the charge ofisophthalic acid.

Example 2 A sample of the tetramethyl ester prepared in Example 1 wasdissolved in concentrated sulfuric acid and warmed on a steam bath for30 minutes. The resulting solution was then poured into cold water andthe precipitated crude acid filtered off. The product was furthersaponified to give an'essentially quantitative yield of3,3',5,5-tetracarboxydiphenylmethane which analyzed as follows:

Calculated for C H O C, 59.3; H, 3.49; neutralization equivalent, 86.Found: C, 59.3; H, 3.65; neutralization equivalent 86.

This tetracarboxylic acidhad a melting point of 346- 350 C.

Example 3 This run was carried out to demonstrate the effect ofincreasing the proportion of formaldehyde to the dicarboxylic phenylcompound. A small glass reactor was charged with ml. 20% oleum, 33.2 g.(0.20 mole) isophthalic acid and 6.2 g. (0.20 mole) paraformaldehyde.The reactants were heated for 6 hours at 120 C., cooled, and then pouredinto a large excess of ice water. The precipitate was filtered, washedwith distilled water and dried on a vacuum oven. Unreacted isophthalicacid was separated by converting the entire crude product to methylesters whereupon the tetramethyl ester precipitated from a methanolsolution and the dimethyl isophthalate remained in solution as describedin Example 1.

Tetramethyl ester of bis(isophthalic acid)methane of melting point196-19 8 C. was obtained as previously described. In this run the yieldof the tetramethyl ester was increased slightly to 85.5% based on thecharge of isophthalic acid. I

Example 4 In this example, a mixture of 200 ml. 100% sulfuric acid, 66.5g. (0.40 mole) isophthalic acid and 6.4 g. (0.20 mole) paraformaldehydewere heated at l17-122 C. for 5 hours. The reactants were cooled andthen pured into an excess of ice water. The crude product whichprecipitated was filtered, washed with distilled water and dried in avacuum oven to obtain 68 g. of material. The reaction product wasconverted to methyl esters by reaction in methanol with hydrogenchloride whereupon the tetramethyl ester prccipitated'from methanol asdescribed in Example 1. This product was purified by recrystallizationfrom cyclohexanone and dried to obtain a diminished yield of 3,3',5,5tetracarbomethoxydiphenylmethane, melting point 196198 C.

During the preparation of the tetramethyl ester in methanol, it has beenobserved that by-product dimethyl isophthalate remains dissolved inmethanol and the tetramethyl ester, the desired product, precipitates inessentially quantitative yield from the solution. In one preferredmethod for the practice of the invention, we charge the dimethylisophthalate directly to the initial reaction. In the concentratedsulfuric acid or oleum medium the ester may be hydrolyzed to the acidwhich then participates in the condensation reaction in the normalmanner.

Example A small steel autoclave was charged with 75 ml. oleum, 28.1 g.(0.145 mole) dimethyl terephthalate and 4.6 g. (0.145 mole)paraformaldehyde. The bomb was sealed and immersed in an oil bath at156160 C. for 3 hours and 45 min. During this interval thorough mixingwas maintained by vigorous vibration of the autoclave. The reactor wascooled and the contents poured into an excess of ice water. The crudeproduct which precipitated was filtered and thoroughly washed with waterand then dried in a vacuum oven. The product was then dissolved byheating with excess absolute ethanol in the presence of a stream ofhydrogen chloride gas. The reactants were maintained at reflux for 30minutes and then cooled. The precipitate which separated was filteredoff, washed with cold ethanol and dried in a vacuum oven. The product, amixed methyl, ethyl ester of bis(terephthalic acid)methane, weight 13.5g., melting point 145- 151 C., gave the following elemental analysis:

Calculated for C H O C, 64.8; H, 6.14; saponification equivalent, 114.Found: C, 64.0; H, 4.97; saponification equivalent, 103; neutralizationequivalent, 0.0.

Example 6 In this example, the procedure as outlined in Example 5 wasfollowed, except that instead of 20% oleur'n, 75 ml. of 65% oleum wascharged to the autoclave along with the dimethyl terephthalate andparaformaldehyde. In this run an improved yield of 19.8 g. of the mixedmethyl, ethyl ester of bis(terephthalic acid)methane of melting point149153 C. was obtained. This product gave the following elementalanalysis:

Calculated for C i-1 0 C, 64.8; H, 6.14; saponification equivalent, 114.Found: C, 63.84; H, 5.00; saponification equivalent, 103.

Example 7 It has been demonstrated that the tetramethylesters of ournovel tetracarboxylic acids can be readily prepared by heating the acidwith excess methanol in the presence of gaseous hydrogen chloride. Thetetramethyl ester of any particular acid can then be converted to otheralkyl esters by an ester interchange reaction. By this means, mixedesters can be prepared as well as other higher esters.

A distillation pot was charged with 100 ml. of n-butanol and 20.0 g. ofthe tetramethyl ester of bis(isophthalic acid)methane and the solutionsaturated with hydrogen chloride gas. This reactor was then attached toa 15 inch distillation column equipped with a reflux head and thereactants heated to reflux. Methanol, liberated by the ester interchangereaction, was removed from the system operating at reflux temperature.During an interval of 2 hours the pot temperature slowly climbed from105 C. to 121 C. and the reflux temperature at the head,

climbed from 60 C. to 117 C. as part of the combined methanol wasliberated and removed from the system.

Excess butanol was then stripped off under reduced pressure and thecrude tctrabutyl ester was dissolved in benzene, washed with water,dilute aqueous sodium bicarbonate solution and additional portions ofwater. The benzene solution was then treated with activated charcoal toremove color forming impurities. The charcoal was filtered off and thebenzene evaporated at reduced pressure. An esentially quantitative yieldof product was obtained. Elemental analytical data indicate that thetetrabutyl ester of bis(isophthalic acid)methane was contaminated withpartial methyl ester. The viscous product had an extremely low vaporpressure at room temperature and appears to be particularly usefulas alow volatility type plasticizer for vinyl type polymer, e.g., polyvinylchloride. Analytical data for this butyl ester is as follows:

Calculated for C H O C, 69.8; H, 7.75. Found: C, 67.5; H, 7.0.

The calculated saponification equivalent for the tetrabutyl ester is142, and for the tetramethyl ester; the mixed ester was found to have asaponification equivalent of 126, thus indicating a 62% average butyland 38% methyl ester content for the mixed ester.

Example 8 The ester interchange reaction between the tetramethyl estersof our tetrabasic acids and other higher alcohols, as described inExample 7 can be used in the preparation of any higher esters. In thisrun, the interchange reaction was conducted in' the presence of excess2-ethylhexanol using hydrogen chloride as catalyst.

A charge of 100 ml. of 2-ethylhexanol, 18.5 g. of the tetramethyl esterof bis(isophthalic acid)methane was saturated with hydrogen chloride andcharged to a distillation set-up. As the interchange reaction proceededat a temperature within the reaction pot from 100 C. to 187 C., methanolwhich was liberated was removed from the system during an interval of 2hours and 45 minutes. The resulting 2-ethylhexyl ester was isolated andpurified as described above. This extremely viscous ester, havingextremely low vapor presures at normal temperatures, is of particularinterest as a plasticizer for vinyl type resins. This ester wassubmitted for elemental analysis with the following results:

Calculated for C H O C, 74.3; H, 9.6; saponification equivalent, 198.Found: C, 70.3; H, 8.3; saponification equivalent, 152.

The saponification equivalent data indicate 54% of the ester exists asthe 2-ethylhexyl ester and 47% as methyl ester.

Thus, a mixed methyl, Z-ethylhexyl ester was obtained. By modificationsof this procedure, i.e., longer reaction times, excess charge of higheralcohol of from about 2 to 13 carbon atoms, etc., various mixed esterscan be prepared. The ester interchange reaction can also be conducted inthe presence of a basic catalyst. In many instances the use of alkalinematerials, instead of an acidic catalyst, results in a nearlyquantitative conversion to the desired higher-alkyl ester.

In many instances to obtain desired solubility and volatility propertieswe vary the ratio of methyl ester to higher alkyl ester content. Forexample, we can convert the novel tetracarboxydiphenylmethanes tomono-methyl trihigher-alkyl esters, di-methyl di-higher-alkyl esters,and tri-methyl mono-higher-alkyl esters, where alkyl represents ahydrocarbon radical of from 2 to 13 carbon atoms. It will be understoodthat the esters can also be aralkyl esters such as those prepared frombenzyl alcohol, phenethyl alcohol, etc., and such esters are includedwithin the purview of our invention.

Example 9 A sample of the mixed methyl and ethyl esters of his-(terephthalic acid)methane prepared in Example 5, 6.0 g., was refluxedin aqueous KOH solution to saponify the esters. After an extended refluxthe reaction mixture was cooled, and acidified to precipitate the crudetetracarboxyli-c acid. The acid, crystallized from dimethylformamide,M.P. 292-4 C. analyzed as follows:

Calculated forC H O z C, 59.3; H, 3.49; neutralization equivalent, 86.Found: C, 60.3; H, 3.53; neutralization equivalent 87.

The analogous tetracarboxylic acid derived from pht'nalic acid and asource of formaldehyde can also be prepared following the proceduresdescribed above, the his- (phthalic acid)methane is more diflicult toobtain in a highly purified condition due to the similar solubilitycharacteristics of the phthalic acid and the tetracarboxylic acid.

The esters of our novel polyfunctional compounds are convenientlyprepared by ester interchange since in one preferred procedure thetetramethyl ester is prepared during the isolation and purification ofthe products from the condensation reaction. However, it will beunderstood that the tetracarboxylic acid can be converted to atetraester in the presence of an acidic catalyst, e.g., benzenesulfonicacid, in esentially quantitative conversion.

While the invention has been described with particular reference topreferred. embodiments thereof, it will be appreciated that variationsfrom the details given herein can be effected without departing from theinvention in its broadest aspects.

We claim:

1. The process for the preparation of a tetracarboxydiphenylniethanewhich comprises heating from 2 hours to about 20 hours at 100 C. toabout 200 C. a dicarboxyphenyl compound with a source of formaldehydeselected from the group consisting of formaldehyde, paraformaldehyde,trioxymethylene, and dimethoxymethane, in a concentrated sulfuric acidmedium.

2. The process of'heating from 2 hours to about 20 hours at 100 C. toabout 200 C., a compoundselected from the group consisting of benzenedicarboXylic acids and derivatives of said benzene dicarboxylic acidswith a source of formaldehyde selected from the group consisting offormaldehyde, paraformaldehyde, trioxymethylone, and dimethoxymethane ina concentrated sulfuric acid medium to prepare atetracarboxydiphenylmethane. 3. The process of claim 2 wherein thesulfuric acid medium is a concentrated sulfuric acid solution contain- 82 hours to about 20 hours at 100 C. to about 200 C. a compound selectedfrom the group consisting of isophthalic acid and isophthalic acidderivatives with a source of formaldehyde in an acid medium ofconcentrated sulfuric acid of at least sulfuric acid strength.

5. The process for the preparation of bis(terephtha1ic acid)methanewhich comprises heating from 2 hours to about 20 hours at C. to about200 C. a compound selected frorrrthe group consisting of terephthalicacid, and the esters and acid chlorides of terephthalic acid with asource of formaldehyde in an acid medium of sulfuric acid of at least90% sulfuric acidcontent.

References Cited by the Examiner UNITED STATES PATENTS 2,712,543 7/1955Gresham et al 260346.3

FOREIGN PATENTS 416,544 7/1925 Germany.

OTHER REFERENCES Le Blane et al., J. Org. Chem. vol. 26 (1961), pages4731 to 4733.

Welch et al., J. Am. Chem. Soc. vol. 73, pages 4391-3 (1951).

LORRAINE A. \VEINBERGER, Primary Examiner. CHARLES B. PARKER, LEONZITVER, Examiners.

1. THE PROCESS FOR THE PREPARTION OF A TETRACARBOXYDIPENYLMETHANE WHICHCOMPRISES HEATING FROM 2 HOURS TO ABOUT 20 HOURS AT 100*C. TO ABOUT200*C. A DICARBOXYPHENYL COMPOUND WITH A SOURCE OF FROMALDEHYDE SELECTEDFROM THE GROUP CONSISTING OF FORMALDEHYDE, PARAFORMALDEHYDE,TRIOXYMETHYLENE, AND DIMETHOXYMETHANE, IN A CONCENTRATED SULFURIC ACIDMEDIUM.